Broadband Speed Faults: How to diagnose?

July 2nd, 2007 at 14:00 by James

One of the more common questions that we are asked by our customers is “Why is my Broadband slow?” Which in itself is, of course, a perfectly reasonable question. Unfortunately, finding the answer isn’t always quite as easy! We have customers on fixed rate products and max products and the diagnosis on both is quite different. This is predominantly owing to the distinct lack of useful diagnostics available for us on the fixed rate products, but fortunately, on the max (upto 8Mbps) services, there are considerably more diagnostic tools available that help us to diagnose speed issues, as well as tools available for the customer. I’ll be focusing on this product in this posting as at least two thirds of our customers are on the upto 8Mbps product with us.

So where do we begin? I think it’s a sensible starting point to set out clear expectations when dealing with speed issues. The first and most fundamental point is that upto 8Mbps means just that. It is not guaranteed. Broadband is extremely dependent on your distance from your local telephone exchange. This is true for signal issues and in extreme cases may result in receiving a Broadband service impossible. Maximum obtainable speeds are dependent on this also. The further you are from the exchange, the poorer quality a Broadband signal you will be able to receive from said exchange. The better the quality of signal, the greater will be the maximum expected throughput speeds, although this also depends on how “busy” your local exchange is, but that’s another issue we can delve into later.

One of the most useful tools available to our customers is the BT Speedtester, which gives a reasonable amount of information about the limitations applied to the Broadband connection from a speed perspective. Please note, if you have a broadband speed fault you will need to complete two tests – once the first has completed please click ‘further diagnostics’ and fill in the details requested before completing the second test. If this is not completed our faults team will not have access to the results.

The speed tester is still somewhat in its infancy so can be a little unreliable at busy times of the day. Here’s an example of a result from the Speedtester.

So, as you can see, you are presented with four main pieces of information. Your upstream and downstream synchronisation speeds (this is the speed at which your modem or router is connecting with the BT Exchange), your IP Profile and your actual throughput speed as recorded by the test. For the majority of speed faults, the upstream synchronisation speed can practically be ignored, unless it reports speeds significantly below 448Kbps. The IP Profile is the speed at which BT have restricted your connection to, as they believe that this is the fastest speed that you can receive whilst also receiving a stable connection. The IP Profile is the maximum speed that you will be able to get in a speed test.

The downstream synchronisation speed is extremely important. This is the speed at which BT use to calculate your IP Profile. We have a table on our website which shows you’re the relevant synchronisation speeds versus the appropriate IP Profile speeds, which you can find here. You can also see your current profiled speed on our network, which is designed to mirror BTs IP Profile and is updated twice a day. See this here.

Unfortunately the IP Profile is not updated on a real time basis. BT take your lowest downstream synchronisation speed (hence the importance of this as I mentioned earlier) over a three day period and then assign the appropriate IP Profile. Here’s where the problems can occur. Downstream line synchronisation can and does fluctuate.

There are various factors that can cause line synchronisation to drop and fluctuate. Most commonly these factors can relate to faulty filtering, a suspect modem or router or poor internal wiring. The best setup for any Broadband connection is always to have your modem or router connected into a filter and then for your filter to be connected to your master socket, which is normally the first socket into your house from your road. It is also imperative that every used phone socket in your house has a filter attached, as failure to do this can cause interference between the analogue (normal voice phone) and digital (Broadband) signals. There are also additional factors that can come into play such as poor weather, exchange and line related problems and even things like street lights, central heating and Christmas lights!

If your modem or router does drop synchronisation and it regains synchronisation at a lower level, then BT will change your IP Profile speed to reflect this change in reported synchronisation speed within 75 minutes. In extreme cases, this can cause the IP Profile to be set as low as 135Kbps when a resynchronisation event equal to or lower than 160Kbps happens. This does happen to the best of us, including myself, who lives on the same street as his exchange! BT do have in place something they refer to as “Blip Logic”, which is supposed to mean that they will only force a change in profile speed should there be two resynchronisation events lower than the current profiled speed. Unfortunately, this does not always seem to be the case. So, as you can imagine, it is always fundamentally important to ensure that you setup ensures the highest level of signal, by connecting to your master socket (also known as the NTE5) as I outlined earlier. This will result in any potential resynchronisation events being less likely, thus increasing the chances of maintaining a sustained speed at the highest possible level.

One of the other factors when it comes down to diagnosing Broadband speed problems is a further connection attribute of the noise margin. Because with Max, BT push the limits of your connection as far as it can go, they will try to attain the highest synchronisation speed with a target noise margin of 6dB. For the majoirty of lines, this will work absolutely fine, especially for those closer to the BT Exchange. However, some lines, especially the longers ones, will experience more “noise”. This can be caused by a number of factors on the line, be it poor quality telephone wiring (external), street lighting, transmitters, interference from electronic devices (pylons) and so on. BT will then assign a higher noise margin to the Broadband connection. For every 3dB increase in noise margin, this will result in approximately an 800Kbps reduction in synchronisation speed. Also, this is often one of BTs first measures when trying to fix an intermittent fault. So if we raise a fault to BT for an intermittent connection, they will often raise the target noise margin by 3dB to increase stability on the line at the detriment of speed. So this is also another thing to consider when trying to work out what kinds of speeds you *could* be receiving.

So, obviously so far I’ve covered what our customers are able to do and see and the suggested actions and precautions that can be made to cope with the perceived flaws of the service and what information is available to them. We also have our own diagnostic tools available to help to troubleshoot this kind of problems and give a more detailed level of information to help our customers understand the cause of the problems that they experience. In the next part of this posting, I’d like to give you an insight into the systems that we use and the information that we gain from these. We predominantly use systems called “Actuate” and “Woosh”. I’ll start by showing you a standard report from Actuate and the information that we can see from this.

The main points of interest that I would usually take from these reports are generally the current profile, the synchronisation rate and the dates and times of resynchronisation rates. From these we are able to easily point at the relevant resynchronisation events and show a customer at exactly when their modem or router suffered a blip and the speed at which the resynchronisation occurred. What is also useful is when there are a large number of “blips” which would often point towards an issue with internal wiring or poor hardware, which means that we are then able to suggest various troubleshooting ideas to our customers.

What is also of interest is the interleaving state. Interleaving is a function on the max product that increases the stability on a line, but increases the latency of a connection, which is generally of interest to our customers that enjoy online gaming. This allows us to see if BT have removed interleaving from a line once we have raised an order for them to do so.

The other main diagnostic tool that we use is one called “Woosh”, which is essentially a suite of various different tests. The ones I would predominantly use are the “DSL Status Check” and a “One Shot Check”. A lot of the information is repeated, but various tests have their own uses. Here’s a DSL Status Check:

From my point of view, I tend to use this check to show the current synchronisation speed when checking against the last report resynchronisation event as reported in Actuate. This is useful as we can then inform the customer of what speeds they should expect to receive should this level of synchronisation be maintained for a period of 3 days or more.

The One Shot Check is by far a more conclusive all-round test (no screenshots this time I’m afraid as it contains a level of sensitive information), which can be used to diagnose intermittent connection issues, as well as having a use when looking into speed related faults. Whilst it does generally give similar information to that of the DSL Status Check, it does also show how long the current connection has been maintained for, which coupled with our RADIUS (authentication) server allows us to see the length of connection and the current synchronisation speed. It also shows us the number of reconnections in a given time frame. An intermittent connection is likely to have a few low resynchronisation events, thus causing the IP Profile speed to be low. As such we can suggest internal wiring and hardware checks, which will hopefully result in increased stability and as such, an increase in speed.

Unfortunately, the one thing that we’re not able to gain a massive amount of information on is exchange contention. Each exchange has a finite amount of bandwidth which Broadband users are able to use simultaneously. For busy exchanges there can be a noticeable slow down during peak times of the day. Whilst we are given a RAG (Red, Amber, Green) report for all of BTs exchanges, this is merely a guideline and not a definitive answer. You can see the current status of your exchange here.

Our systems of traffic management also need to be considered. Whilst these usually would not impact pure browsing speeds. However, on our Broadband Your Way product line, where our customers have requested a fixed usage amount (as opposed to Pay As You Go), speeds are restricted to 128Kbps. There are also potential speed restrictions on legacy Broadband Plus and Premier products, which can result in speeds being restricted should the usage allocations be exceeded. This should be considered when looking into slow speed results from both our and the customers end.

Well, that’s pretty much all I could possibly ever write on this subject, but should there be any further developments on the Broadband services that we provide, I shall endeavour to update further! For an even more definitive guide to the Broadband Max service then please do read the guide on our portal.

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entry was posted by James on Monday, July 2nd, 2007 at 2:00 pm and is tagged with and is posted in the category Plusnet News. You can follow any responses to this entry through the RSS 2.0 feed.
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62 comments on "Broadband Speed Faults: How to diagnose?"

That is an excellent exposition on Maxdsl and its pros and cons. I would like to see a mention of the time it takes for SNR Margin resetting by BT and if this is still unpublished. I am investigating getting a different router because the Binatone ADSL 2100 (supplied by Plusnet) will not speak to any version of the DMT Tool. Even if BT decide to reduce the present three day wait for increasing the profile speed this will not do much for customers like me in the country still suffering with a raised SNR Target after a major electrical storm over 2 weeks ago.

Unfortunately IP-Profile does not control the sync speed making it a rather useless component of the broadband spectrum.
You can have a high sync speed and a high noise level with a low IP-Profile and hence low download speed giving a very poor performance. This can only add to customers annoyance unnecessarily.

Yes that's true but it would be much better if the IP Profile controlled the sync speed. At the moment it controls download speed which is pretty much useless.
You can sync at 8028kbps and have an IP Profile controlled download speed of say 1000kbps with an awful connection. The IP Profile does nothing constructive.
In my case, the connection is stable at ca. 6000kbps so I have to adjust to this each time the modem is rebooted.
I could ask for the min noise margin to be increased but then if I had to reboot during the peak period I would have a low sync speed which would lower the IP Profile and limit download speeds for several days until the IP Profile was reset.
I know it's not the fault of PlusNet but it's a pity you don't have more influence with BT Wholesale or whoever it it that seems to put customers last.

Agreed. It would be really handy to have influence over sync and SNR profiling like we do with Tiscali. I'm not sure about changing the IP Profile, but if we had for example, a target maximum sync speed, that would be really useful.

Ultimately, I think we'll be waiting a very long time for this as it would take BT ages to implement it and also there would be the risk (from their perspective) of some ISPs misusing the tool and ultimately creating more faults and flooding their call centres.

I have a situation where clamping the sync speed could be to our advantage. Our SNR appears to change frequently between two levels. As a result with a fixed noise margin the sync rate is either likely to be excessively slow if it syncs while the line is poor or unstable if it syncs while the line is good. From experience I'm fairly sure I know what max rate the line can sustain.

How about some guidance on what sync speed should be expected for a given line length and/or line attenuation? I understand of course that not all lines are created equal, but some typical figures would be very helpful. I'd particularly like some guidance on what PlusNet would consider to be unacceptably poor speed for a given line (assuming of course faults with the customer's internal wiring are ruled out).

Unfotunatly I was directed here from my metronet account and the "see this here" link takes me to the plus net login screen and not my profile. I am supposed to be on adslmax thro' metronet, but the BT speed test result screen does not show this.

As a 'normal' person, this gibberish makes little sense to me, and I am not interested in the technicalities of providing me with the internet connection that I am paying for. I am not paying PlusNet for the privilege of diagnosing their faults, or anyone else's! I pay PlusNet for up to 8MB, and get less than 1MB, that's stealing in my view. If I bought up to 8 cans of beans, or up to 8 pairs of socks, and didn't even get one, then I would be just as angry and disappointed! PlusNet blame BT, however my previous four providers also blamed BT for my getting between 1.5MB and 3.5MB when I was paying for 8MB. PlusNet are the worst provider I have had yet. I am totally bored with these crooks blaming each other, when all I want is what I am paying for, or something even close to it!

A great article which really goes into the issues with ADSL Max. What I'd like to see is some comparison made with the earlier products limited to 512Kbps, 1Mbps, and 2Mbps - I've had poor performance since moving 'upgrading' (pardon me while I die laughing) to ADSL Max from a 2Mbps ADSL account. Both with Plusnet. I haven't moved, nor changed provider or router so what is the story here? I'm getting 15db of NR on the line so am I losing 2.4Mbps of feed to start with? I have an open fault with Plusnet but we've just got the point of a new analyst asking for a repeat of the original tests so I don't hold out much hope. Is there an option to 'downgrade' to a fixed speed? One possible cause is a BT line fault which resulted in me losing my phone for four days after a cable two miles away was cut. Is it possible that their fix wasn't up to it?

sent letter complaing of the very slow connection to broadband as requested, we are still waiting for a reply to confirm a date for an engineer to contact us to sort the problem, perhaps plusnet is slow with
everything? might be a sign to change server

Thanks for your time on the phone just now. As I mentioned, it's really important to have filters on all the telephone sockets that you use, because otherwise it can cause the broadband signal to worsen, causing slower broadband speeds. Please do let us know how you get on.

I was assured that you would check my Broadband speed in your e.mail dated 21.12.08.My BT download speed continues to be a miserly 470kbt.I would appreciate if could help to augment the speed or alternatively could you let me know if I can get in touch with somebody who will be able to help.

I've taken a look into this and there seems to be a restriction happening at the exchange causing the speed problems. I've asked one of our faults team to investigate this and contact BT for you. You can follow the progress of this by looking at the ticket I've just raised on your account.

Hifolks,
I have just discovered that my download speeds have suddenly dropped to 479Kbps (Measured Mar 1 & 3 on My Broadband Speedtester) Normally I have been getting anything from 1874Kbps(Sept 14) to 2814Kbps(Feb 12) since joining PN. This new figure is suspiciously like Dr.Mahapatra's figure, is BT up to something???

Thanks for that. I tried the BT Test but got bogged down by not giving them the login details that they expected. It looked as though they wanted a email address but perhaps I got it wrong and they wanted another one. It was the similarity between what I now get and those by Dr. Mahapatra's figure that triggerwed me off. I might add that Kelly is looking at a malfunction that I have with an apparent disconnection between the Begin button on My Broadband Speedtester panel and the running of the test. I get over this by typing in the speedtester suffix to the URL.

Why is my line only 1.5mb when I have 8mb broadband, it states that my exchange i should get 4mb which would be kind of good but not what i'm paying for. But for it to be only 1.5mb is lousy.
You need to talk to BT or you guys turn the tap on more.

James
Great article as far as it goes, but can you explain a bit more about the BT DLM that seems to have taken control of my service!
In particular :-
1. Does the DLM look for loss of synch/router disconnection prior to dowmgrading the downstream service?
2. If so how many disconnections in what time period cause the DLM to intervene and downgrade the service profile?
3. Does the DML downgrade service by increasing the suggested operational noise margin for the router and reducing the line profile?
4. If so by how much is the noise margin increased and how much is the dowmstream speed reduced?
5. if the service is downgraded (reduced line profile) assuming no actual fault, how can it be improved and how long does this take?
6. If 2 applies are the criteria reduced or maintained before a further reduction in downstream speed is made?
7. Can this automatic process be disabled. When the service was apparently failing to perform (through multiple disconnections) I experienced no problems and would not have complained about apparent disconnections?
8. Since no one told me I should not turn my router off, can the initial 10 day test period be re-started?

Thanks for your comment - I think if I tried covering everything the article would probably have never ended and it was a touch on the verbose side to start with!

To answer your questions:

1 - The DLM will downgrade the speeds (ie the IP Profile) based on the speed of resynchronisation events, so yes.
2 - I believe (and this is certainly thw case on the ADSL2+ product) that it is more than one disconnection within the space of 15 minutes.
3 - If there are multiple disconnections, then yes this can, and does occur (quite commonly).
4 - It's generally done in 3dB increments and you're normally looking at a decrease of about 800Kbps in sync speed per 3dB increase in SNR.
5 - Hah - With some difficulty. It involves raising a fault to BT who are generally only happy to reamend the "target SNR" if they are happy that the fault has been rectified.
6 - There would be no reduction in criteria. Again, this is all determined on the synchronisation speed.
7 - Unfortunately not. It's designed to ensure that a "stable" internet connection is maintained and we have no way of bypassing the DLM.
8 - It can be, but it's unlikely to be beneficial.

I've been on plusnet for a couple of years now and my speeds have always been excellent. Recently I haven't been able to get the speeds I used to get (getting as low as 110 kbts), after long investigations and speed checks it turns out plusnet have updated their network and lots of consumers have been left with very poor speeds. See plusnets repsonse dated November 2009 at:

I have a dsl connection rate of 7328 kbps but an ip profile of only 250kbps and a down load rate of 214 kbps.

I'm totally confused as to how I get my ip profile back, had a BT engineer round today who checked everything, changed master socket and some external wiring and tested and said all ok but plusnet needed to change my profile. Plusnet say they can't they have to wait for BT to raise profile, when I ring the support centre I get a different story every time ie yes its with fault desk we will change it, then ring later we can't change it, its down to BT and it goes on...a whole month now and I just seem to be back where I started. Can you explain the process do BT and plusnet both have to do something.

Paul, I would recommend seeking direct support for this via a thread in the forums, or a ticket in your customer portal. You will get a better response from this than a comment in a blog like (which is easily overlooked!). Having said that, if the profiles haven't been reset, but BT did some major work on your line, I believe that Plusnet just got the ability to re-initiate the 10 day training period (Like when you first signed up), which will reset all parameters and assess the line on its current status rather than its historic one!! Since this is so new, most Customer Service guys might not be aware of this option being available yet. I would create a thread in the community support forum http://community.plus.net/forum/index.php/board,3.0.html and state the problem, and ask there. Quote any existing ticket numbers you have in the thread, so that some from Plusnet can take a look when the pass by. Hope you get it sorted.
Mike

All very confusing. Wish some sort of notification had been given of problems at 'base.' I assumed my slow speeds were due to high number of Gb inmy picture and same with emails. Now I can't send or receive or even open existing in inbox. Then again, I assumed twas my fault and fiddled with settings- like you do!!!

Sorry to hear you've had problems, if you pop over to our Forums (http://community.plus.net/forum/) and ask for assistance either myself, another member of staff or even one of our helpful customers will be able to give you some assistance.

for over a week now i am getting intermitten conectionsd and low speed. my ticket is with faults department and nothing seeems to be done to improve the issue. on speed tester site, i m getting the following;
Download speedachieved during the test was - 144 Kbps
For your connection, the acceptable range of speedsis 100-500 Kbps.
Additional Information:
Your DSL Connection Rate :544 Kbps(DOWN-STREAM), 444 Kbps(UP-STREAM)
IP Profile for your line is - 350 Kbps

as i am paying premium for up to 20 Meg , this is not satisfactory especially as virgin are providing fibre optic cable to me!!

@taz999 your IP profile is restricting your throughout speed, almost certainly the result of the intermittent connectivity problems you've been having. If you post your support ticket reference here then I can take a look and see if there's anything I can do to help?

Like many others (see Plusnet and other forum postings), I am now getting about 100kbps. About 200k this morning; nearer 50k last night. Why do we all have to raise a ticket? This is clearly not an individual issue.

Whilst it might not appear to be an 'individual issue', the reason behind your problems will be something specific to *your* line and the environment in which it operates. In order to establish the cause for the speed reduction we need to look specifically at your set of circumstances. The best way for us to do this is for you to raise a fault ticket on your account - http://faults.plus.net

My ticket is active. But there appears to be a more serious issue.
Problems have been going on long enough now that I can say the following. (Bear in mind that I live in a rural area with little business handled by my local exchange.)
1. When I lose a DSL signal, it often happens on the hour or the half hour. As such, it appears to be a system matter, not accident.
2. During school terms, the signal often goes dead at 16.30 (+- 30mins), and sometimes at 09.00, and frequently overnight. I suppose this relates to boosts in load.
3. During school holidays, speeds are generally slower. I suppose this relates to load.
4. Previous advice from PlusNet was to switch the router off/on if the signal died. (I now understand that this actually lowers the speed I will get, which is not what I want atall.)
Your advice piece above, and response to my ticket, help me obtain symptomatic relief (avoiding having BT's system lower my speed), which is, as you say, specific to my line.
I am wanting a better understanding of the root cause of the problem, which is why the DSL signal gets cut (hundreds of times in the last 12 months, with a frequency that reached several times each day just before the start of the school summer holidays). Then I will know whether to persist with what, for £20 per month, has been an appalling service. In view of other forum contributions it is extremely difficult to believe that this matter is line specific. If it is a matter of BT provision, it is one that should be of PlusNet's concern, rather than cause me a lot of my time.

Additional clarification.
When I say the DSL is dead, I mean that the router still shows a DSL light indicating connection, but there is no internet (as was the case this morning). Sorry if my terminology has not been correct.

@Woodsider, I'm going to add some further detail to your support ticket shortly, however to address the points you've raised here:

1. Just to clarify, it's your PPP session that is being lost by the sounds of things and *not* your DSL signal (DSL signal is the connection to the exchange). Having said that, the signal *is* being dropped quite frequently as a result of you turning your equipment on/off - whether it's overnight, or to fix things when you lose connectivity, it is playing havoc with the IP profile of your line which over the last fortnight has varied from 135kbps right up to 3000kbps.

2. Over the last fortnight the PPP session has been dropped at the following times:

3. Quite possibly, although with the fluctuations in your IP profile, I'd be very surprised if you were to notice subtle performance differences due to exchange/network congestion.

4. This kind of relates to the response I've given for the first question. You'd be much better off accessing the router console and manually reconnecting from there instead of rebooting the router. Doing things this way doesn't drop the DSL signal and therefore shouldn't affect your IP Profile (although you'd need to stop turnign things off at night).

I'll go into more detail on your support ticket however I'm inclined to agree with what my colleagues have advised at this point which is to try another modem/router (can you borrow one off somebody?)to rule out a hardware fault/misconfiguration.

It seems that for one reason or another, your router is not always re-establishing a PPP session when you're disconnected. Would be helpful to know what router it is you're using?

My router is "BT Voyager 2100" supplied by PlusNet.
Some of my response to the above has been included in a lengthy addition to my ticket.
Of more general interest is that I have apparently been losing internet access while not (according to the list above) losing my PPP session. (And the PPP session sometimes does not close even when my router has been left switched off.)
Also of more general interest is that the data you have supplied confirm that such losses of internet happen on the hour. There is nothing in this house that switches at these hours. Further, the question of which hour is one that changes according to whether it is school term, though there is nobody of school age within about 500m of this rural outpost.
No idea what can be done with that information.

@Woodsider It seems that your connection has become a lot more stable since those last results, but if you are still experiencing difficulties then I would maybe try a different router and if that doesn't help then visit faults.plus.net for some further help.

Concerning the importance of filtering. Above, we read "... your filter to be connected to your master socket, which is normally the first socket into your house from your road. It is also imperative that every used phone socket in your house has a filter attached ...".

It transpires that much of the noise on my line (and most of its variability) comes from my only, and unused, extension. So, adding a filter only between used extension sockets and the attached equipment, as James suggest, is not sufficient. The logical answer appears to be to disconnect all extension lines from the back of the plate (which has the master socket) and then reconnect them from a branch off the phone's line from the filter, but I haven't tried that yet.

Bob Pullen (12 Aug.) is right. I (14th) was wrong.
While the end results are just a few apparent problems (speed, losing internet, ...), the circumstances are individual.

It's not that the list of possible issues is much longer than I knew of. It's rather that many issues are negligible or even dormant when they occur alone. (Who cares if internet can't autoconnect after dropping, if it never drops?) So, by the time you are spurred to action you probably have several issues, and the number of possibilities in your circumstance is given by all the possible permutations.

If you are just starting to work on a broadband problem, look out for several problems not just one.

But ... there are exceptions. Because problems are assumed to be individual, those that are not can be particularly infuriating, and you may never find out whether they have actually been solved.

One possible wider problem is congestion within Plusnet's realm. If you raise a ticket, Faults may well respond after the congestion has cleared, and set you on a wild goose chase of checking router, telephone wiring, other home gadgets, ... which is difficult to object to, even if you are sure it's pointless.

Then there are BT problems. Even when several of us with different ISPs on the same exchange lost internet access, BT's procedure was not to look at the exchange until engineers had checked individual lines. That may be why we all waited over 48hours before BT personnel admitted to an exchange problem. Even then the exchange checker was Green ("no problem"), and afterwards there was no feedback via Plusnet to say what had been done.

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